i run my a052's at 28f /27r psi hot 255 on a 10inch wheel, only for timed events. As mentioned earlier they're good for about 1.5-2 laps max before they get slidey. I compete locally in a 3 lap format anyways so i just run a cooldown lap on 3 and pit.
i run my rt660's at 30f / 29r psi hot 255 on a 9inch wheel. which i use for general hpde. Running the pressure any higher the rt660's just slide around too much specially in the rear on trail brake and early throttle, the rt660's will have none of it. however they seem quite durable im getting excellent wear and lots of days out of them.

Those seem to give me the best results.
-3.5 front camber, - 3 rear 800/700lbs with karcepts bars/mcs 2w remotes

I also agree on lower pressure's ive never really liked any 200tw tire above 32psi hot

 

Agree on this. For autox, I tend to run 28/27 on A052s. They can go lower of course without rolling over, but they get even more numb and the response goes down as does overall grip. Much higher and I start to see an increase in run times. Running pretty much the same setup as you other than I am running a stock rear bar with a Karcepts FSB and I am runnign on a revalved set of TCKlines (Koni 8242's).

For HPDE I also run the RT660s and have liked them so far. Great wear and are faster than the RS4 so a nice balance of an HPDE tire. I run mine at 28/27. I tried 30 and 31 and it only seemed slower. I put down the fastest times at 28 psi and have pretty much just stuck to that.

 

I'm fine with my A052 (255 on a 9") anywhere between 28 and 30 psi. I don't think they really get slower down to 26 but they feel squirmier and roll over more. Above 32 psi, it feels that traction drops off. In colder weather, I like to run 26-28 PSI.

I haven't run RT660s yet but people generally like higher pressures in them than with A052's or old RE71's.

I've heard from multiple people now that the Kuhmos run low psi.

 

I also run 3-lap time trials, one warm-up lap followed by 3 timed laps, compete based on best lap of the three. Have run A052s, Nankang CR-1/CR-S, and RE71RS, 245s or 235s on 9" wheels on the BRZ. I've always been able to get three good time trial laps out of them (four laps counting the warm-up) running 34psi hot. Sometimes 1st timed lap is fastest, sometimes 2nd, sometimes 3rd. Tire pressure does take a few laps to build, so going out on 27psi cold with a gentle warm-up lap, figure 2nd lap (1st timed) average probably ~30psi, 3rd lap (2nd timed) ~32psi, 4th lap and on ~34psi. Definitely my 1st timed lap is at lower pressure than the last one, but there's no correlation between lap # and lap time for me so no indication that lower pressure is any quicker for me.

Every tire is different, every car is different, every driver different, but from my experience plus examination of tire test data, there's a broad range of pressures that will yield similar lap times. For me I haven't seen anything to suggest that running lower pressures will gain me any time. Always see people trying to see how low they can go though...

 

makes sense on a mac strut front car with poor front geometry but good rear traction and rear suspension geometry. the s2k is the opposite of that, the earlier i can get onto throttle the faster my times are. when the pressure's high the car just slides around on entry and exit in the rear and my times show.
probably the biggest dependency is track layout. lots of straights means more cool down time between corners, or how many corners that come in succession and the time between the corners. my local tracks are particularly hard on tires without much cooldown time provided for tires or brakes.

 

I tend to go faster as well when I can get on the throttle sooner in the BRZ...
Anyway back when I ran my S2k in time trials, at even higher hot pressures (36psi fully developed hot) I still see that my lap times are consistent over 3 timed laps, fast lap could be 1st, 2nd or 3rd timed lap. After warmup, 1st lap ~32psi, 2nd lap ~34psi, 3rd lap ~36psi. If lower pressures were "faster" I should see some correlation...

Seems to me people are *assuming* that "lower pressure => more grip". IMO for these cars there's a *very* broad range you can run, at least that's been the case for myself in 240Z, S13, S14, S2000, LS3 FD, and BRZ. I've just never seen a strong correlation between pressure within a reasonable range, and lap times. It's not like these are high-hp high-downforce formula cars that are sensitive to 1/2-psi increments...

 

Whether it be autocross or track, it is all about making the straights "longer". So making the car more planted on corner exit is of course huge. It sounds simple, but this is something that comes up a lot on autox instruction sessions. On track, is a big part of going faster. And yes, there are "Straights" on autocross courses. A straight is simply a place where you can be mostly flat out. The sooner you can start adding throttle out of a corner, the more speed you carry through the whole acceleration zone. At the end of the day, we are "simply" trying to make it so we are hard into the throttle the highest % of the time we are out there when it comes to outright track times

Also, Zdan is correct that lower pressure does not equal more grip. There is a pressure range that the tires will like best. Anything higher or lower will be less grip. You can decide if you want less grip and squirmier feel or less grip and sharp feel, but outside the sweet spot is going to be slower either way. It may be on that track this range is "broad" but it is not on an autocross course. The range seems to be much narrower in that specific application. But I will say I have seen a marked difference in my car on track, same day, same track between starting at 27 psi and 31 psi. At 31 psi I was about a second slower. 27 or 28 feels and runs about the same. Then jumped to 31 to try a bigger change and was just slower across the board. Especially affected the rear as I was just not able to put down power as soon out of the slower corners with them raised that high.

There are tons of variables here though. As NCRX mentioned, some tracks give you very little cool down time between corners and others have long straights. Not to mention alignment and lots of other variables here. Lower pressures also means the tires heat up faster. That may or may not be a good thing depending on what you are doing.

 

The pressure discussion is interesting. Tire pressure does two things, 1) changes contact patch and 2) changes effective spring rate.

If you are making massive changes to tires pressure without taking temperature readings you are not getting the information needed to make the right next move. If you are going way over 32 psi with most radials you need to look at springs rates. Also without tire temps you don’t know if you’ve got the right setup.

I use pressures to fine tune. Any change in there shouldn’t be seconds a lap faster.

 

Also changes *lateral* "spring rate", more significantly than vertical spring rate since lateral "spring rate" of the suspension is very stiff.

If you aren't correlating tire temp profiles with lap times, knowing tire temps is only partly beneficial. I'm sure most here know that chasing even temps across the treads is not going to be "fastest" but some track-goers with a pyrometer are aiming for that... But also, chasing a temp profile based on others results isn't necessarily going to home in on "optimal" for you either.

FWIW my BRZ setup is very much a street/track compromise, so for sure spring rates are quite soft for track at 4.4F/5.3R (4.0F/3.0R wheel rates). Going to much stiffer f/r swaybars helped a bit...

Exactly. For most production car setups it's not like there's a magical sweet *spot* pressure that's going to be hugely faster than + or -1psi from there. If you are at a place where a modest change in pressure yields big changes in lap times, you are probably way off the middle of the optimal pressure range. For me, over 3 hot laps after a slowish warmup lap, I'm seeing very similar lap times even as pressure is rising from ~30ish to ~34ish psi.

Track conditions are typically changeable throughout the day, and also most of us are not going to be perfectly consistent session to session. Never assume that if you make a change to tire pressures, that any changes in lap times next session out are strictly from that pressure change.